What if Quantum Computers Used Hard Drives Made of DNA?

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What if Quantum Computers Used Hard Drives Made of DNA?

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You’ve heard the hype: The quantum computer revolution is coming. Physicists say these devices will be fast enough to break every encryption method banks use today. Their artificial intelligence will be so advanced that you could load in the periodic table and the laws of quantum mechanics, and they could design the most efficient solar cell to date. And they’ll be here soon: Writing in Nature earlier this month, Google researchers said they anticipate the first commercial quantum computers in five years, and the company wants to build and test a 49-qubit—that’s “quantum bit”—quantum computer by the end of this year. Some experts say that a 50-qubit computer could outperform any conventional computer.

But there's a big problem: By its nature, you can't save or duplicate information on a quantum computer. All that computing power is of little use if you can't back up your work. You can convert quantum data and put it on a traditional storage device, but all that converted data takes up a lot of space. So physicists are hunting for reliable, super-compact hard drives made of new materials—including DNA.

Quantum computers are so powerful exactly because of their data density. A classical computer reads, stores, and manipulates bits: 1’s and 0’s. A quantum computer uses qubits: tiny quantum objects that can be in two states—both 1 and 0—at the same time, as long as you’re not looking at it. And if you control a quantum particle in a superposition of two states, you can perform tasks in parallel, which speeds up certain computational tasks exponentially. That speed won’t improve your Netflix experience or make Microsoft Excel more bearable, but it will be much faster at running search algorithms or simulating complicated systems like organic materials or the human brain.But the weirdness of quantum mechanics has its drawbacks. Its laws permit superposition, but they also forbid anyone from copying a quantum particle. “It’s called the ‘no-cloning theorem,’” says physicist Stephanie Simmons of Simon Fraser University in Canada. Say that a quantum computer programs an atom to be in a specific quantum state that represents a set of numbers. It is physically impossible for the computer to program another atom to be in the exact same quantum state.

So Simmons proposes a roundabout way of storing quantum data: First, you’ll need to convert it into binary data—translating the numbers that describe quantum superposition into simple 1's and 0's. Then, you store that converted data in a classical storage format. In other words: hard drives. Super compact ones, because the size of each quantum data file from a 49-qubit computer will be on the scale of 40,000 videos.

To store that much data, quantum computer developers need new data storage technologies, Simmons says. Commercial drives aren't compact enough right now. A single quantum file would occupy a stamp-sized area on a solid-state hard drive.

So one alternative storage contender is DNA. Published earlier this month in Science, scientists demonstrated a method that could store 215 petabytes, or 215 million gigabytes, in a single gram of DNA. At that density, all of humanity’s data could fit in a couple pickup trucks. Unlike conventional hard drives, which only store data on a two-dimensional surface, DNA is a three-dimensional molecule. That extra vertical dimension lets DNA store much more data per unit area.

Plus, it lasts a long time. "Think about your CDs from the '90s," says computer scientist Yaniv Erlich of Columbia University, who worked on the research. "They're probably a bit scratched, and you can't read the data accurately. But DNA can store information for a very long time. We can read DNA from skeletons thousands of years old to very high accuracy."

Another super-compact technology encodes bits in single atoms. Last week, researchers at IBM published that they stored a bit in a single atom and successfully read the data back. To do this, they embedded holmium atoms on a chip and used electronics to control the direction of the inherent magnetic field produced by each atom. They found that they could control the atoms independently when they were spaced just a nanometer apart. So basically, it's possible to encode one bit per atom. You can't get more dense than that, says physicist Chris Lutz of IBM. Commercial hard drives store a bit in at least 100,000 atoms—and even a DNA base pair is made of some thirty atoms.

Both of these methods, like quantum computers themselves, are years from being commercial technology. DNA is expensive to synthesize and takes a long time to read out. And to store data in single atoms, you have to keep the atoms extremely cold—close to absolute zero—because otherwise, the atoms will interfere with each other and overwrite their data. On top of that, the quantum computing crowd will need to develop algorithms to efficiently compress and convert quantum data to binary—and then design hardware to execute those algorithms.

Even as Google prepares to run its 49-qubit quantum computer, it’s still not clear how quantum computers will back up their information. "I see huge challenges coming our way," says Simmons. Because if quantum computers don’t back up their data, autosave won't be coming to the rescue.

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